Power transmission



P 1944-- F. T. HARRINGTON 2,345,973

POWER TRANSMISSION Filed 0012. ll, 1941 INVENTOR FERRIS T. HARRINGTON W 1. 7 ATTORNEY Patented Apr. 4, 1944 POWER TRANSMISSION Ferris 'r. Harrington, Detroit, Mich., mm. to

Vickers Incorporated, Detroit, Mich, a comeration of Michigan Application October 11, 1941, Serial No. 414,554

3. Claims.

This invention relates to power transmissions, particularly to those of the type comprising two or more fluid pressure energy translating devices, one of which may function as a pump and another as a fluid motor.

The invention is more particularly concerned with a power transmission system of the type'incorporating what is termed a metering-out, flow rate control valve comprising an adjustable throttle together with a pressure responsive compensating valve for maintaining a constant pressure drop through the throttle. Valves of this character are customarily used in power transmission systems for producing a reduced feed rate of a machine tool slide or similar device which is hydraulically operated;

Ithas been found that, where the flow regulating valve is placed on the outlet side of the circuit and is relied upon as the only obstacle to free flow from the exhaust side of the cylinder, some difllculty has been experienced at the time the slide is started into a feeding movement from rest. This difficulty lies in the inability of the compensating flow control valve to immediately assume its normal regulating position. During the time interval that this requires, fluid is dirooted to the motor at a greater than normal rate, causing the slide to jump ahead at the beginning of a feeding movement. This is particularly objectionable in machine tools where, for some reason, it may be necessary to stop'the slide during the middle of a cut and then, if the feeding movement be resumed, theslide jumps ahead momentarily causing breakage of the cutting tool. This difiicultyhas been avoided inthe past only by continued caution on the part of the operator to remember that, when stopping the slide in the middle of a out, he must first back the tool away from the work slightly before resuming the feeding movement.

It is an object of the present invention to provide an improved circuit which overcomes this difflculty- A further object is to provide in a power transmission system of this character a back-pressure valve beyond the flow regulating valve together with special internal connections in the flow regulating valve such that, when the slide is at rest, the compensating valve assumes a closed position.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the aecom panying drawing wherein a preferred form of the present invention is clearly shown.

In the drawing: 4 The single figure is a diagrammatic view of a power transmission system incorporating a preferred form of the present invention.

There is indicated at I!) a pump adapted to be driven by a suitable prime mover such as an electric motor i 2. The pump ID has a suction conduit l 4, for withdrawing fluid from a tank l6, and a delivery conduit i8. A relief valve 20, on pump i0, is adapted to pass fluid to tank i6 through a conduit 22 whenever a, predetermined maximum pressure'is exceeded in the pump.

The delivery conduit i8 extends to a directional valve 24 where it opens into a valve bore 25 through an annular pressure port 28. Spaced along bore 26 to the right of port 28 are three annular ports 30, 32' and 34, while to the left of port 28 are corresponding ports 36, 38 and 40.

.A valve spool 42 mounted in bore 26, and slidable between five positions, has formed thereon three lands 44, 46 and 48 for controlling communica-' tionbetween the various ports. Spool 42 has drilled passageways 50 therein connecting the pressure port 28 to ports 34 and 40, which constitute tank ports, when it is in the position shown. A hand lever 52 is connected to the left end of spool 42 I positions of spool 42' by yieldably engaging in one of three annular grooves 58, or 62 formed on the valve spool to the right of land 44.

The right end of valve spool 42 has a reduced diameter portion 64 which projects into a chamber 66 in end cap 54. The portion 64 carr es thereon two spring abutment washers 38 between which is placed a spring 18. Washers 6B are movable toward but not away from one another. The chamber 66 has formed therein a shoulder 12 against which the righthand washer 68 abuts when spool 42 is moved beyond its feed right position, and a shoulder 13 a ainst which the lefthand washer abuts when the spool is moved beyond its feed left posit on.

The two" ports 30 and 36 constitute cylinder ports and are connected by conduits Hand 18 to the head and rod ends, respectively, of a cylinder 18. A piston reciprocably mounted in cylinder 18 has a rod 82 which may be operatvely connected to the tool or work slide of a machine tool.

A conduit 84 connects two tank ports 34 and 40' of valve 24 to tank l8 through a back-pressure valve 86, the spring 8801' which is. heavy enough to maintain a low pressure in conduit 84 for a purpose later to be described.

The two ports 32 and 38 of valve 24 are connected together by a conduitv 90 which extends to an inlet connection 92 of a hydrostatic flow control valve 94. The connection 92 opens into a valve bore 96 through an annular port 98. A valve seat I is formed at the lower end of bore 96 where it opens into a chamber I02. A hydrostatic valve I04, slidable in bore 96, has an enlarged bevel portion I06 on the lower end thereof for controlling communication between port 98 and chamber I02. When valve I04 is in its uppermost position, as shown, portion I06 seatsat I00 to close port98 from chamber I02.

For the purpose of controlling valve I04, a piston I08 is formed on the upper end thereof and mounted in a control cylinder H0. A spring II2, lighter than spring 88 of valve 86, in the upper end of cylinder IIO, abuts piston I08 and tends to move valveI04 downwardly to unseat portion I06.

The chamber I02 is connected by a passage I I4 to an outlet port I I6 of valve 94 where a conduit II8 extends therefrom and connects into conduit 84. A throttle valve I20, rotatably mounted in a bore I22, is interposed in passage I I4 and serves as an adjustable restriction to flow through thelatter. Throttle I20 is adjustable by rotation of a hand dial I24. Any fluid leakage along the space between throttle I20 and bore I 22 passes to a drain chamber I26 which is connected directly to the tank I6 by a conduit I28.

The upper end of cylinder H0 is connected by a passage I30 to the drain chamber I 26 while the lower end is connected by a passage I32 to chamber I02. The passage H4 is in communication with drain chamber I 26 and the tank conduit I28 through a restricted bleed-oil passage I34, which e isless restrictedthan passageelflwttle I24 is adjusted for maximum flow.

In operation, with the parts in the positions shown and the motor I2 driving pump I0, fluid is withdrawn from tank I6 through conduit I4 and to the head end of cylinder 18. The rod end of cylinder 18 is placed in communication with the inlet port 98 of valve 94 through. conduit I6, ports 38 and 38 of valve 24, conduit 90 and connection 92.

As conduit 84 is no longer receiving fluid from pump I0, pressure therein and in chamber I02 andthe lower end of cylinder IIO will be relieved through restriction I34 and conduit i 28 to tank I6, thereby permitting spring II2 to lower valve I04 and open port 98 to chamber I02.

Accordingly, with the pump delivery being directed to the head end of cylinder I8, the piston 80 will move to the left with exhaust fluid from the rod end following the path previously described to port 98 of valve 94 from where it will flow through chamber I02, passage II4, throttle I20,- restriction I34 and conduit I28 to tank. Since this volume is small, the restriction I34 imposes negligible resistance.

Valve I04 will move downwardly until the rate of flow from port 98 into chamber I02 equals the rate of fluid flowing from chamber I02 through throttle I20 to tank.

The hydrostatic valve I04 maintains a constant pressure drop across throttle I20, in the wellknown manner, which results in a constant feed rate of piston 80 regardless of variations in resistance thereto. The excess pump volume not accepted by the motor is bypassed to tank through relief valve 20, or the pump I0 may be of the type which automatically reduces its output in response to pressure'built up during the feeding stroke.

If at any time during a feeding stroke the need arises to stop piston 80, valve spool 42 is returned to the position shown. The pump delivery will again be directed to tank through conduit 84 and valve 66. Pressure created in chamber I02, by back-pressure valve 86, will cause hydrostatic valve I04 to rise until bevel portion I06 seats. When valve 24,is again shifted to the left, to continue the leftward feed stroke of piston 80, the restriction I34 will relieve pressure in chamdelivered by conduit I 8 to the pressureportfilibf cemepifliaspwflgzfescribed. Thus, it will be valve 24. From there the fluid is passed to the -tank I6 by passages in spool 42, ports 34 and 40, conduit 84 and the back-pressure valve 86. The full pump volume is thus circulated to tank at a low pressure determined by the spring 88 ofvalyg 86.

This pressureiin conduit 84 is transmitted through conduit I I8, port llipf valve 94, passage H4 and throttle-l20 to'chamba' mland by passage- I32 to the lower end of cylinder H0; With the upper end of cylinder I I0 open to tank, it will.

be seen that the pressure in. chamber I02 and the lower end of cylinder IIO acts on the lower faces of valve I04 and piston I08, respectively, to hold bevel portion I06 seated at I00 against the resistance of spring II2. Flow through the bleed-off restriction I34 from passage II4 to tank is not suflicient to drop this pressure to the point where spring I I2 could open valve I04.

To effect a feeding stroke of piston 80 and its rod 82, the lever 52 of valve 24 is moved, for example, to the left until detent 56 engages groove 80 of spool 42. The spring 10 is not compressed so he spool will remain in its feed left position.

The tank ports 34 and 40 are blocked from all of the other ports ofvalve 24. Ports 28 and 38 are now in communication with ports 30 and 36, respectively. This directs the pump delivery from port 28 to port 30 and through conduit I4 7 seen that, upon s ting of-pistgn gfl, the flow of exhaust fluid from cylinder I8 is graduallyincreased from zero to the maximum, as determined by the setting of throttle I20, as hydrostatic valve I04 is opened by spring I I2. will be seen that the piston is started without racing or jumping. This permits the piston 38 to be restarted, even though its operated tool or slide is engaging the work, without first having to back it up, as heretofore has been necessary to prevent tool breakage by the sudden jump or racing of the operating piston.

If it is desired to have piston 80 move to ,the right on a feed stroke, the operation is similar to that just described except that valve 24 is reversed. Valve spool 42 is shifted to the right until detent 66 drops into the right end of groove 62. The righthand spring abutment washer 68 moves up against shoulder I2- of chamber 66 but does not compress spring I0. The spool 42 is thus held in its feed right position. Ports 28 and 32 are placed in communication. with ports 36 and 30, respectively. Pressure fluid is directed to the rod end of cylinder 18 through conduit I6, and exhaust fluid from the head end passes through conduit 14 and valve 24 to conduit 90. Valve 94 functions the same as when piston 80 wasmoving to the left. g

If it is desired to return piston 80 to the left or right at a rapid rate, the valve spool 42 is Thus it the right until detent 56 is past groove 62.

Spring will be compressed making it necessary that lever 52 be held in rapid traverse righ position as long as a rapid movement of piston 80 is desired. If the lever is released, it will return to feed right" position.

In the frapid traverse right position of spool 42, port 38 is opened to the tank port 40 while all other connections remain the same as when piston 80 was moving to the'right at a feed rate.

The pump in delivers fluid to the rod end of cylinder 18 through conduit 16 while exhaust fluid from the head end passes through conduit 14, ports 36 and 32, conduit 90, ports 38 and 40, conduit 84 and valve 86 to tank [6.

The valve 941s bypassed and piston 80 moves to the right at a rapid rate. Valve 86 maintains valve and having a compensating valve therein of the type which opens fully whenever flow through the valve is interrupted, and means for directing fluid bypassed around the motor while thelatter is stopped to a point between the backpressure valve and the outlet of the flow regulating valve whereby the compensating valve is maintained closed during periods when the motor is stopped.

2. In a hydraulic power transmission the combination of a pressure fluid source, a fluid motor,

a directional control valve for selectively direct-' ing fluid to and from the motor for either directhe low back pressure in conduit 84 to hold hydrostatic valve I04 closed. Similarly, in rapid traverse left position, port 32 is opened to tank port 34, leaving the other connections the same as for feed left.

Whenever piston 80 is stopped, or operating in rapid traverse, hydrostatic valve I04 will close port 98 from chamber "12. Thus it will be seen that piston 80 may be started from any stopping point at a feed rate, regardless of its'previous action, without-racing or jumping. 4

It will be noted that, while the piston is stopped, any leakage inherent in valve 24 will not drop the pressure in either end of cylinder 18 as is'the case with prior circuits. Thus, any leakage across the lands 46 and 48 -at either side of port 36, for example, will take place from 90 and I8, respectively, toward conduit 16 since the former conduits carry the'light pressure which is maintained by back-pressure valve 86. In this way it'is assured that the oil on the advancing side of the piston 80 is always under a slight pressure at the very last instant before a feeding motion is resumed.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to'be understood that other forms might be adopted, all-coming within the scope of the claims which follow.

What is claimed is as follows:

1. In a hydraulic power transmission the combination of a pressure fluid source, a fluid motor, a directional control valve for selectively directing fluid to and from the motor for either direction of operation thereof and having a neutral position in'which flow from the source is bypassed around the motor, fluid supply .and return conduits connecting the source to the motor with the directional control valve therebetween, a back-pressure 'valve interposed in the return conduit between the directional control valve and the source, a flow rate control valveiinterposed in the return conduit ahead of the back-pressure interrupted, means forming a bypass around saidcontrol valve to obtain the other said speed,

tion of operation thereof at either of two dif-.

ferent speeds and having a neutral position in which flow from the source is bypassed around the'motor, fluid supply and return conduits connecting the source to the motor with the directional control valve therebetween, a back-pressure valve interposed in the return conduit between the directional control valve and the source, a flow rate control valve interposed in the return conduit ahead of the back-pressure valve to obtain one of said speeds and having a compensating valve therein of the type which opens fully whenever flow through the valve is and means for directing fluid bypassed around the motor while the latter is stopped to a point between the back-pressure valve and the outlet of the flow regulating valve whereby the compensating valve is maintained closed during periods when the motor is stopped.

3. In a hydraulic power transmission the combination of a pressure fluid source, a fluid motor, a. directional control valve for selectively, directing fluid to and from the motor for either direction of operation thereof and having a neutral position in which flow from the source is bypassed around the motor, fluid supply and ;re-

turn conduits connecting the source to the motor with the directional control valve therebetween, a back-pressure valve interposed in the return conduit between the directional control valve and the source, a flow rate control valve interposed in the return conduit ahead of the back-pressure valve and having a spring-loaded compensating valve therein of thetype which opens fully whenever flow through the valve is interrupted, and means for directing fluid bypassed around the motor while the latter is stopped to a point between the back-pressure valve and the outlet of the flow regulating valve, said back pressure valve having a higher pressure setting than the pressure required to overcome the spring load on the compensating valve, whereby the compensating valve is maintained closed during periods when the motor is stopped.

FEBRIS '1'. HARRINGTON. 

